This invention relates to a transmission method for efficient transmission of a binary signal, such as a two level facsimile signal.
Heretofore, there have been proposed, as a two-level facsimile signal coding system, (1) a run-length coding system in which a signal obtained by scanning is converted into a time series train and then the magnitudes of the run lengths of white and black are successively coded alternately with each other for transmission and (2) a system in which signals of plural, for example, two scanning lines are simultaneously coded all together. The system (1) does not utilize at all the property that facsimile signals have a high correlation in a direction perpendicular (vertical) to the scanning line direction; therefore, the compression efficiency is low. The system (2) makes use of the correlation in the vertical direction with respect to the signals of a set of scanning lines to be coded at a time but does not utilize the correlation to signals of this system other scanning lines; consequently, the compression efficiency is higher than that of the system (1) but no sufficient compression effect is achieved, since this system does not fully use the two dimensional correlation among adjacent scanning lines.